OpenJDK Performance Fix: How Replacing /proc Parsing with a Syscall Eliminated 400x Slowdown
By
bluestreak
Crackling crust, pillowy middle. The kind of bagel that earns a second cup of coffee.
Summary
The article analyzes a specific OpenJDK commit that dramatically improved Java performance by replacing inefficient /proc file parsing with a direct syscall. The author examines how a 40-line code change eliminated a 400x performance gap in thread CPU time measurement on Linux systems. The fix involved replacing complex file I/O operations with a single clock_gettime() system call, revealing a 20-year-old optimization opportunity in the Linux kernel's thread CPU time tracking. The article provides technical details about the commit, explains the performance implications, and discusses the broader lesson about avoiding unnecessary file operations for system information retrieval.
Key quotes
· 4 pulledThe diffstat was interesting: +96 insertions, -54 deletions. The changeset adds a 55-line JMH benchmark, which means the production code itself is actually reduced.
static jlong user_thread_cpu_time(Thread *thread) { pid_t tid = thread->osthread()->thread_id(); char *s;
The article reveals a 20-year-old optimization opportunity in the Linux kernel's thread CPU time tracking.
The fix involved replacing complex file I/O operations with a single clock_gettime() system call.
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